The present invention relates to a system and method to control an internal combustion engine coupled to a torque converter, and in particular to adjusting engine output to improve drive feel.
Internal combustion engines must be controlled in many different ways to provide acceptable driving comfort during all operating conditions. Some methods use engine output, or torque, control where the actual engine torque is controlled to a desired engine torque through an output adjusting device such as with an electronic throttle, ignition timing, or various other devices. In some cases, such as during normal driving conditions, the desired engine torque is calculated from the amount of depression of an accelerator pedal. In other conditions, such as idle speed control, the desired engine torque is calculated based on a speed error between actual engine speed and a desired engine speed. Some attempts have been made to use this torque control architecture to improve drivability during deceleration conditions such as when a driver releases their foot to the minimum accelerator pedal position, known to those skilled in the art as a tip-out. During a tip-out, the driver is indicating a desire for reduced engine output.
One system that attempts to use speed control during deceleration conditions operates the engine in such a way as to maintain constant engine speed during slow moving or stopped conditions. In this system, the engine is controlled to a constant speed taking into account the loading from the torque converter. The loading from the torque converter is calculated based on the engine speed and turbine speed. Engine speed can be controlled to a constant level during deceleration to adsorb energy from the vehicle and assists in vehicle braking. Further, as turbine speed increases, the desired engine speed is reduced to provide even more engine braking. Such a system is described in DE 4321413A1.
The inventors herein have recognized a disadvantage with the above approach. In particular, when the accelerator pedal is released and subsequently engaged, the prior art system exhibits poor drivability due transmission gears lash. For example, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, or clunk, resulting in poor drivability and customer dissatisfaction. In other words, the engine first exerts a positive torque through the torque converter onto the transmission input gears to drive the vehicle. Then, when using the prior art approach during deceleration, the engine is driven by the torque from the transmission through the torque converter. The transition between these two modes is the point where the engine is producing exactly zero engine brake torque. Then, at this transition point, the gears in the transmission separate because of inevitable transmission gear lash. When the gears again make contact, they do so dynamically, resulting in an undesirable impact.
This disadvantage of the prior art is exacerbated when the operator returns the accelerator pedal to a depressed position, indicating a desire for increased engine torque. In this situation, the zero torque transition point must again be traversed. However, in this situation, the engine is producing a larger amount of torque than during deceleration because the driver is requesting acceleration. Thus, another, more severe, impact is experienced due to the transmission lash during the zero torque transition.
An object of this invention is to provide a method for determining when the vehicle is operating in or near the transmission lash zone.
The above object is achieved and disadvantages of prior approaches overcome by a method for estimating when a vehicle is near a transmission lash zone, the vehicle having an internal combustion engine coupled to a transmission via a torque converter having a speed ratio from torque converter output speed to torque converter input speed, the method comprising the steps of: indicating when the speed ratio is within a predetermined range; and determining that the vehicle is near the transmission lash zone in response to said indication.
An advantage of the present invention is that it is possible to make other engine control features aware that the vehicle is operating in a region where transmission gear separation may occur. Thus, other engine control features can take action to minimize effects of transmission gear separation.
In another aspect of the present invention, an object is to provide an engine output control system for easing transitions through the transmission lash zone.
The above object is achieved, and problems of prior approaches overcome, by a vehicle control method for a vehicle having an internal combustion engine coupled to a torque converter, the torque converter having a speed ratio from torque converter output speed to torque converter input speed, the torque converter coupled to a transmission, the method comprising the steps of: indicating when the speed ratio is within a predetermined range; and in response to said indication, adjusting an operating parameter to control a change in an engine output to be less than a preselected value.
By using signals already available, it is possible to provide a real-time estimate of the transmission lash zone, or zero torque point. With this information, it is then possible to transition through the transmission lash zone gently by controlling engine output so that xe2x80x9cclunkxe2x80x9d is minimized and fuel economy and emissions are optimized. In other words, the present invention utilizes the torque converter characteristics in the following way. Because these measurements are readily available, adjusting engine output according to the present invention near the transmission lash zone allows much improved drive feel since the effects of gear separation are minimized. Further, by using turbine speed and engine speed, effects from road grade, vehicle mass, temperature, and other factors are inherently considered without complexity or addition computation.
An advantage of the above aspect of the invention is improved drivability.
Another advantage of the above aspect of the invention is improved customer satisfaction.
Yet another advantage of the above aspect of the invention is improved fuel economy.
In yet another aspect of the present invention, the above objects are achieved and disadvantages of prior approaches overcome by a control method for a vehicle having an internal combustion engine coupled to a transmission via a torque converter having an input speed and an output speed, the method comprising the steps of: determining a speed ratio across the torque converter based on said input speed and said output speed; and controlling an engine operating parameter at a preselected rate when said speed ratio is within a predetermined range.
By controlling an operating parameter in this way, it is possible to gently pass through the transmission lash zone, thereby improving driver comfort.
An advantage of the above aspect of the present invention is improved drive comfort as a result of less severe transmission gear separation.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.